The English Civil War was started by concerns over a King Charles I. First concern was based on his absolutist tendency. He believed in the right of the King to make whatever decision he wished, and in his wars he began to tax whomsoever he chose, usurping the powers of Parliament to do so. This angered Parliament and also the people, seeing that their rights and liberties were being trampled upon without even a thought of discretion by Charles I.
Second concern was due to belief that he was a Catholic, seeing that he had a Catholic wife and that he resisted the Puritan’s wishes to reform the Anglican Church. Though not himself Catholic, his marriage to the French Princess raised a good deal of concern amongst his Protestant subjects, who feared another return to Catholicism.
The two sides in this war turned out to be the Levelers and the Roundheads; the Levelers supporting Parliament in their fight against Charles I, and the Roundheads supported Charles. The Levelers were eventually able to defeat Charles I at the Battle of Preston. After arresting Charles, they beheaded him for his usurpation of power, shocking the world by their boldness in restoring freedom to England. And that, is the (very) rough overview of the English Civil War.